ARL Postdoc Fellowship
ARL Postdoc Fellowship

Weapons and Materials Research Directorate Research Areas

Surface Science

Surface Processing by Directed Beams and Plasmas

Advisor:  JD Demaree and JK Hirvonen         

Key words: ion beams and bombardment, surface modification, plasma processing, polymer processing

Opportunities exist to study the surface modification of materials by energetic directed beams and plasmas, utilizing keV-MeV ion beams, pulsed excimer laser beams, magnetron sputtering, as well as vacuum/atmospheric plasma processing. Current research is focused on surface modification studies on multifunctional materials including flexible [polymeric] substrates for studying and enhancing surface mediated mechanical, chemical, and optical properties. Experimental facilities include a 1.7 meV tandem accelerator coupled to an excimer ablation system, a 0.2-2 keV ion beam assisted (e-beam) deposition system, and an RBS/PIXE analysis chamber. Facilities also include a multi-magnetron sputter source system and coupled rf plasma generator as well as  other conventional [XPS, AES] surface analytical capabilities

Reference
Nastasi M, Mayer JW, Hirvonen JK: in Ion-Solid Interactions: Fundamentals and Applications. Cambridge: Cambridge University Press, 1996

Laser Desorption and Surface Scattering Studies

Advisor:  RC Sausa            

Key words: laser spectra, laser-induced fluorescence, mass spectra, molecular collisions, solid surfaces, surface scattering

Laser-induced desorption and collision-induced dissociation (CID), resulting from supersonic molecular-beam molecule-surface scattering, can be used to examine chemical and dynamical processes that occur on solid surfaces. These processes are important in the identification of surface species for possible sensitive detection of energetic materials, and in understanding surface erosion and coating. The objective of this research is to study the surface scattering and laser-induced desorption of simple NOx or metal-containing compounds from Ag, Pt, or Fe surfaces.

Laser-induced fluorescence, resonance-enhanced multiphoton ionization with time-of-flight mass spectrometry, or quadrupole mass spectrometry are used to

  • identify the scattered or desorbed species.
  • measure their rotational, vibrational, and transnational energy distributions.
  • ascertain the mechanisms for laser desorption, CID, and epitaxial growth.

Dedicated equipment includes an ultrahigh vacuum apparatus equipped for ion detection and laser-induced fluorescence; a data acquisition and analysis system; and several pulsed, ultraviolet-visible lasers.

In Situ Characterization of Novel, Pulsed Laser Deposited Thin Films

Advisor: RC Sausa                            

Key words: laser-induced fluorescence, pulsed lasers, thin films, high-temperature superconductors, ferroelectricity, coatings, laser ablation

This research centers on the use of laser-induced fluorescence (LIF) and associated techniques to understand the pulsed laser deposition process and to establish a plume chemistry data base, which will facilitate the deposition of a variety of novel thin films with greater reproducibility. Films of interest include high-temperature superconductors, ferroelectrics, and protective coatings.

A pulsed laser is used to ablate the target of interest, and the ejected material is deposited on a heated substrate. We study the surface ablation, nucleation, and growth mechanisms by varying the laser wavelength, pulse energy, ablation spot size, repetition rate, and chamber pressure. A second laser, which is time delayed from the ablation laser, is then used to probe the important chemical intermediates in the plume by LIF and stimulated emission.

We also use emission spectroscopy to identify electronically excited species. Ex situ thin-film characterization is performed by profilometry, atomic force microscopy, and x-ray diffraction. Available equipment includes several excimer lasers, Nd:YAG laser-pumped dye laser systems, deposition chambers, computer interfaced data acquisition and analysis systems, assorted detectors, electronics and electro-optics, and equipment for analyzing the deposited films.

Proposals are also welcome that focus on numerical modeling of the experimental data using detailed chemical mechanisms.